When a primary amine bearing one or more beta
hydrogens is treated with methyl iodide, followed by
aqueous silver oxide, followed by heat, the primary amine is
converted to an alkene. This reaction is known as Hofmann
elimination.
Elimination reactions of 4º-ammonium salts are termed Hofmann eliminations.Bimolecular Elimination of Quaternary Ammonium Ions is hofmann
elimination reaction .(E2)
Since the counter anion in most 4º-ammonium salts is
halide, this is often replaced by the more basic hydroxide ion
through reaction with silver hydroxide (or silver oxide).
halide, this is often replaced by the more basic hydroxide ion
through reaction with silver hydroxide (or silver oxide).
The resulting hydroxide salt must then be heated (100 - 200
ºC) to effect the E2-like elimination of a 3º-amine.
ºC) to effect the E2-like elimination of a 3º-amine.
In an elimination reaction ,acidic hydrogen and the leaving group are at beta and alpha position.
The loss of the β-hydrogen occurs preferably from the most unhindered (least substituted) position [-CH3 > -CH2-R > -CH(R2)].
The product alkene with fewer substitutents will predominate or is the major product.
Ester Pyrolysis also obeys this preference.
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